peppennino, great initiative.
- for the SIT/choke preference is for 100-150 mH range as what Ben Mah and others use from the Hammond 193 range. Can the choke be made with two windings, to allow series or parallel - series for the MoFoos and parallel for the SITters?
Note that there are also ideas to mofo with a SIT - and my sim shows the SIT-version has nicer harmonics even though both share the 100% feedback [is the model MR made for the SIT nicer??]
You request a GB. Does the vendor have specs of frequency?
- for the SIT/choke preference is for 100-150 mH range as what Ben Mah and others use from the Hammond 193 range. Can the choke be made with two windings, to allow series or parallel - series for the MoFoos and parallel for the SITters?
Note that there are also ideas to mofo with a SIT - and my sim shows the SIT-version has nicer harmonics even though both share the 100% feedback [is the model MR made for the SIT nicer??]
You request a GB. Does the vendor have specs of frequency?
some chokes are built for mains freq filtering. Also the Hammond I assume. I always doubt if these can be used for 'our' purpose. (but I still have to test my own jig with a real mains freq filter . . )
For their heavy duty chokes, Lundahl uses their standard output cores they also use for the SE-output and SE-coupling transformers . . .
For their heavy duty chokes, Lundahl uses their standard output cores they also use for the SE-output and SE-coupling transformers . . .
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My rule of thumb says is that a 70mH, 5Adc and max 0,7 Ohm Rdc desighn, when wound alternatively on the same core to give 100mH, would be giving maybe max 1 Ohm Rdc and it would allow 2.5-3Adc.
That's fine for me though.
That's fine for me though.
[I have also contacted a builder in Holland. Though I heard nothing back, would it be nice to compare: what would an offer of a four-C core of audio heritage look like at say 20 pairs?]
Hammond 195T5 costs 100euro excl vat and the core is simple mains 50hz transformer type. Not more hi-fi than the one supplied by FIAT
At that price I would go with Lundahl
To have it cheap and good the only solution is biamping
One lufo for bass with simple 50hz core
One small lufo for mid high with smaller choke on a hi-fi core
At that price I would go with Lundahl
To have it cheap and good the only solution is biamping
One lufo for bass with simple 50hz core
One small lufo for mid high with smaller choke on a hi-fi core
I have been querying Chinees mfrs too, with their "nice" metalglass cores; but response was less than luke warm. If we could say, in group-buy, 25 pairs, that should provoke their interest.
Knowing them, they will give any spec you like
albert
Knowing them, they will give any spec you like
[ok ok I just got some fake parts last week again, "power JFETS" .. so I am biased; but I worked there and the people in hangzhou were very nice and honest to me]
albert
I'm interested to build this MoFO and I am not an expert into audio amplifier. I hope I can get some help from here.
I have gone thru all the parts and the only problem to get is the Hammond 193v choke. My location is in South east asia. The closest I can get is from China. I search it and this are what I find out. Please suggest me which one to get.
80mH@50Hz. 3A/0.9ohm (Price is RMN95)
100mH 3A/1.35ohm (RMB170)
65mH 5A/0.414ohm (RMB170)
What are the important to choose the choke for this MoFo? The mH? or A? or Ohm?
I have gone thru all the parts and the only problem to get is the Hammond 193v choke. My location is in South east asia. The closest I can get is from China. I search it and this are what I find out. Please suggest me which one to get.
80mH@50Hz. 3A/0.9ohm (Price is RMN95)
100mH 3A/1.35ohm (RMB170)
65mH 5A/0.414ohm (RMB170)
What are the important to choose the choke for this MoFo? The mH? or A? or Ohm?
As the MoFo design itself uses 50 mH @ many amps DC, the last one should be fine
The higher price than the first one sort of implies the core is larger too. Or has finer/thinner lamination. That is always better.
- 65mH 5A/0.414ohm
The higher price than the first one sort of implies the core is larger too. Or has finer/thinner lamination. That is always better.
I am with the drain loaded choked L'Amp version (I dubbed it Ch'Amp) and have less than 0,8 ohm and one device is over 2.5 Kg. I run it well far under the saturation limit.
Increasing the current has no effect on the sound; my bandwidth is 7 Hz to 75 kHz.
Increasing the current has no effect on the sound; my bandwidth is 7 Hz to 75 kHz.
Finally joining this Mofo party. I reused a pair of Realistic Minimus 11 speakers as enclosures. Heat sinks are from a pair of Dell ADA995 subwoofers. I thought I was going to have to settle for 15V power supplies given the size of the heatsinks. But they seem to handle 1.8A at 19V just fine. I used Kemet ALC10S for the output caps. As you can see they were a little too big to fit on the Mofo boards. The chokes I used are from here 19C1 Power Choke . I measured a 0.5 ohm DCR and they don't list a current capacity. But given it's both physically larger and heavier than a Hammond 193T, I think it was a good buy. I went with the Toshiba TK7J90E fet for it's low COSS and CRSS. The datasheet doesn't list a transconductance figure though.
I actually finished these a week ago but was having trouble with my WBA2018 linestage so couldn't really listen to them. I fixed the linestage yesterday and after a listening sesh I'm very happy with my monoblocks. This is my first foray into class A, so don't have a lot of reference. But compared to my class AB or D amps, the Mofo has a fluidity that makes me want to just keep listening.
I've got a few more preamp builds in mind. I want to try some tube preamps next. Namely Salas' 6V6 preamp, Eric Barbour's Brute Force in a Linestage and an Aikido. Then maybe some SS preamps such as Salas' DCG3 and the Aksa Lender.
Also, I'm curious to hear, from those more knowledgeable about tubes, regarding an EF86 linestage. It seems the Mofo would be perfect in taking advantage of the EF86's high gain
I actually finished these a week ago but was having trouble with my WBA2018 linestage so couldn't really listen to them. I fixed the linestage yesterday and after a listening sesh I'm very happy with my monoblocks. This is my first foray into class A, so don't have a lot of reference. But compared to my class AB or D amps, the Mofo has a fluidity that makes me want to just keep listening.
I've got a few more preamp builds in mind. I want to try some tube preamps next. Namely Salas' 6V6 preamp, Eric Barbour's Brute Force in a Linestage and an Aikido. Then maybe some SS preamps such as Salas' DCG3 and the Aksa Lender.
Also, I'm curious to hear, from those more knowledgeable about tubes, regarding an EF86 linestage. It seems the Mofo would be perfect in taking advantage of the EF86's high gain
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Thanks to thirdicomplex for the tip on the surplus 50mH chokes, I bought a pair myself and built up two monoblock MoFo's using Vgs matched Vishay IRFP240s (my IRFP250s have been on backorder over a month) and salvaged HP 19.5V (measured under load) laptop bricks for power.
I was curious as to the effect of differing choke inductances on the sound. I have 3 different MOTs I wanted to compare to the 50mH "Nebraska" choke. Using a B1K as a preamp and some Klipsch bookshelf speakers as monitors, I swapped out the choke/MOT in the left channel and kept the Nebraska choke on the right channel and did some listening and measuring. I deliberately kept the pot setting on the swapped channel the same for each choke/MOT.
Device DCR Vdrop Icalc Temp
12mH MOT 0.7R 1.09V 1.56A 68C
50mH choke 0.6R 1.02V 1.7A 69C
89mH MOT 0.45R 0.98V 2.18A 73C
"89mH" MOT 0.4R 0.91V 2.27A 78C
The temps were measured with a thermocouple bead right up against the MOSFET. It's clear that currents much above 1.7A are hard on them.
I can't say I really heard a difference in the sound, though the big MOTs may have sounded a tiny bit louder. Of course this was an unblinded test so obviously biased. The relatively low voltage swing of my B1K preamp is probably hindering the potential of the MoFo.
A fun little project! Thank you M. Rothacher for the design! Haven't decided yet if I'm going to build them as proper monoblocks or not.
I was curious as to the effect of differing choke inductances on the sound. I have 3 different MOTs I wanted to compare to the 50mH "Nebraska" choke. Using a B1K as a preamp and some Klipsch bookshelf speakers as monitors, I swapped out the choke/MOT in the left channel and kept the Nebraska choke on the right channel and did some listening and measuring. I deliberately kept the pot setting on the swapped channel the same for each choke/MOT.
Device DCR Vdrop Icalc Temp
12mH MOT 0.7R 1.09V 1.56A 68C
50mH choke 0.6R 1.02V 1.7A 69C
89mH MOT 0.45R 0.98V 2.18A 73C
"89mH" MOT 0.4R 0.91V 2.27A 78C
The temps were measured with a thermocouple bead right up against the MOSFET. It's clear that currents much above 1.7A are hard on them.
I can't say I really heard a difference in the sound, though the big MOTs may have sounded a tiny bit louder. Of course this was an unblinded test so obviously biased. The relatively low voltage swing of my B1K preamp is probably hindering the potential of the MoFo.
A fun little project! Thank you M. Rothacher for the design! Haven't decided yet if I'm going to build them as proper monoblocks or not.
